1. Field of the Invention
The present invention relates generally to long-term testing of components and more particularly to protecting components from Electrostatic discharge (ESD) during long-term testing.
2. Description of the Prior Art
Long-term testing has become more and more important as competition in the electronics field becomes ever more intense. A company's reputation for reliability is a major factor in many customers' purchasing decision. Reliability, in turn, comes largely from improved procedures based on data gathered during long-term testing of components. During these long-term tests, manufacturers can gather important information on modes of failure, and specific component performance, which can provide valuable feedback to improve devices and components.
Unfortunately, long-term testing can expose components to damage from electrostatic discharge (ESD, here ESD is inclusive of discharge events resulting from electromagnetic interference (EMI), for example), that is generated in amounts not possible during realistic everyday operation by the consumer. In order to avoid damaging components during testing, it is important to protect components from ESD.
ESD can occur when sparks or electrical discharge jump from electrically charged objects to an approaching conductive object. ESD can be generated in many ways, such as by friction between surfaces of moving or rotating objects. In particular, it has been well known that assemblers or production personnel who shuffle their feet while walking across rugs may generate a static charge that can damage components. The use of grounding straps has therefore been common for assemblers in the electronics industry.
Production machinery itself may produce static charge. The present inventor has found that even so common an act as the switching on of a Xenon lamp in the testing facility has produced ESD which lead to puzzling failures before the source of damage was discovered.
Disk drive heads are often damaged due to ESD during a long term thermal or other reliability testing. The test may run as long as 1000 hours and it is difficult to keep the heads from any source of ESD for such long time. Possible solutions that have been proposed to protect the heads include the use of back-to-back diodes, and capacitors in parallel. Unfortunately, diodes provide protection only up to 700 mV but disk heads generally are destroyed if 700 mV is applied in 1 nS or longer time constant. Higher values of capacitance provide higher-level protection under fast transitions in the nanosecond range, but a higher value of capacitance also slows down the speed for Quasi-Static measurements in which uniformed fields are applied to each head/device for magnetic performance evaluations. In addition, capacitors offer essentially no protection from slow transients.
Thus there is a need for a system for long term testing of electronic components and devices which allows for production of realistic performance data without exposing components and devices to damage from ESD.